This study was originally designed to test the efficacy of topical cysteamine for the treatment of corneal cystine crystal accumulation in patients with cystinosis. It was started in 1986, and by 1993 the efficacy of cysteamine drops had been established, at which time benzalkonium was added to the formulation as a preservative. In the years that followed, two variations of the formula were studied, neither proving as efficacious as the original. That formula, consisting of cysteamine 0.5% plus benzalkonium, has been used since 2001, and is currently awaiting review by the FDA.